Sinomenine regulates the AKT/FOXO3/GLUL pathway to inhibit pulmonary fibroblast-to-myofibroblast transition via α7nAChR against rheumatoid arthritis associated interstitial lung disease

Rheumatoid arthritis-associated interstitial lung disease (RA-ILD) is a severe extra-articular manifestation with limited treatment options. Identifying anti-arthritic agents that concurrently protect against ILD is clinically significant. Sinomenine (SIN), a natural alkaloid used clinically to treat RA, shows potential anti-fibrotic activity, but its efficacy and mechanism in RA-ILD remain unclear. Here, integrative bioinformatic analyses identified ILD-associated signature characterized by upregulated CHRNA7 (encoding α7nAChR) and downregulated GLUL, specifically in pulmonary fibroblasts and myofibroblasts, and GLUL was a crucial mediator between RA and ILD. In the adjuvant-induced arthritis (AIA) model with pulmonary inflammatory and fibrotic remodeling, the phenotype that recapitulates early-stage RA-ILD, pulmonary ACh and α7nAChR expression were observed upregulated. SIN ameliorated arthritis and pulmonary lesions, suppressed pulmonary α7nAChR signaling, inhibited AKT/FOXO3 activation, restored GLUL expression and improved autophagy-related changes in this model. Microscale thermophoresis (MST), molecular docking and molecular dynamics simulation supported a direct binding between SIN and α7nAChR. In vitro, α7nAChR activation with PNU-282987 promoted fibroblast-to-myofibroblast transition (FMT), whereas its genetic knockdown inhibited FMT, suppressed AKT/FOXO3 activation, and restored GLUL expression in TGF-β-stimulated MRC-5 cells. We confirmed direct FOXO3 binding to the GLUL promoter by ChIP-qPCR. SIN inhibited FMT and regulated the AKT/FOXO3/GLUL axis in an α7nAChR-dependent manner. Pharmacological inhibition and siRNA-mediated knockdown of GLUL abolished SIN-mediated regulation of mTOR-autophagy signaling and FMT. Our findings identify the α7nAChR/AKT/FOXO3/GLUL axis as a novel fibrotic driver and highlight SIN as a potential therapeutic candidate to inhibit RA-ILD by targeting this axis.